The prior art has a number of different types of designs for panels used as screens for sifting aggregate and other particulate matter according to particle size. For example, a woven wire panel in the form of a grid or matrix comprises one type of screen panel available. Such a woven wire matrix is stretched over a bucker bar support arrangement to hold the screen under significant tension.
Another type of screen known in the art is one typically comprising multiple abutting modules made of, or coated with, elastomeric material. Such modules are typically plates or molded panels with a plurality of perforations and made of a material such as rubber or polyurethane.
Both of these types of screen designs have significant drawbacks when evaluated according to a number of accepted criteria. First, the size and configuration of the openings or perforations through which smaller particles of the material are to pass is a significant factor if particles jam or clog the openings.
An undesirable situation may arise if excessive clogging of any one of a plurality of sifting or sieving panels occurs because of the configuration of the openings or perforations. In such a case, the operator must suspend sifting operations until the clogging is rectified. In accomplishing this with respect to one of multiple sifting decks, removal of other decks may be necessary. During such a cleaning operation, the entire process of use of the sieving equipment halts. This may be costly.
A second factor to be considered is durability or longevity. Because of the highly abrasive environment in which sifting screens typically operate, deterioration can be quite rapid. Not only does this involve increased cost incident to replacement, but downtime can occasion significant costs.
A third factor is the cost of the screens. Wire mesh screens are relatively inexpensive, but they tend to wear rapidly, particularly when the material undergoing sifting or sieving is abrasive. Sand and gravel are examples of such materials. The rapid wear requires frequent replacement and consequent down time.
On the other hand, polyurethane or rubber screens are perhaps 10-12 times more expensive than wire mesh, but they tend to wear perhaps 10 times as long. An operator of a sieving apparatus must, therefore, balance the high initial cost and high durability of polyurethane or rubber screens against the low cost and durability of wire mesh screens.
The operator must consider the total economic cost. For example, wire might be relatively inexpensive per lineal foot. One must, however, consider other costs. Mere replacement cost, while important, is not the end of the analysis. An operator of such apparatus must consider the cost of more frequent screen replacement. For example, a relatively inexpensive screen with low durability that must be replaced ten times as often as another more expensive construction may in the long run, be either less or more costly than the more expensive structure depending on the difficulty in reaching and repairing or replacing a damaged screen or segment thereof.
When applying these factors to prior art structures, one concludes that a woven wire structure is excellent in terms of open area. In terms of durability or longevity, however, woven wire tends to be very poor. And, while in terms of mere price of the material comprising the screen wire tends to be the least expensive, in terms of total economic realities, it must be replaced frequently and overall economic cost can be significant. As will be able to be seen then, there are many costs that must be borne if one chooses to use a woven wire screen.
In terms of open area, a punched or molded screen made of, or coated with, polyurethane, rubber or another elastomer also leaves something to be desired. In the molding or punching process, there can be burrs that, to one degree or another, can partially occlude the apertures through which passes the particles being processed. Further, while a screen made of such materials is typically quite durable, it is very expensive. In a total economic sense, therefore, such screens may not be desirable.
The art of the design of sifting screens reveals no type of screen that does not have some types of shortcomings. While some of the factors generate good marks with regard to a particular type of screen, such a screen is deficient in other respects making it, in many instances, economically disadvantageous.
The present invention is a screen designed for use in sifting, sizing and classifying sieves which solves problems of the prior art. It is of a unique construction which offers a proposed solution to problems of the prior art.